It is well known to attach rolled goods and other rigid and semi-rigid goods to an underlying surface or substrate through any number of traditional methods including mechanical fasteners such as nails, staples, screws, tacks and brads, and chemical fasteners such as adhesives and cements which cure by volatilization of solvents, heat or chemical reaction. Additionally, Remerowski et. al. (U.S. Pat. No. 5,935,369) and Krzeszowski (U.S. Pat. No. 4,123,305) teach methods of bonding rolled goods to a work surface through induction bonding. However, in many applications, especially carpet seaming, it is undesirable to effect a bond between the rolled good and the underlying substrate or intermediate, in the case of a carpet and the intermediate carpet padding, while creating a seam bond between opposing edges of the rolled good or of adjacent pieces of a rolled good. While stitching of seams is common for most rolled goods applications involving fabrics and textiles, stitching is not always practical or possible, especially in applications where the presence of a visible seam would be unsightly as on a large tapestry, canvas or the like.
In order to address concerns relative to seaming of rolled goods without stitching, a number of different technologies and methods have been devised. For example, simple heat activated tapes comprised of a backing and a layer of a hot melt adhesive on one or both sides of the backing have been developed for butt end and overlap seaming, respectively, of generally thinner fabrics and textiles or overlap seaming of thicker fabrics and textiles. These tapes are activated in place by passing a traditional consumer iron over the site of the seam.
The heat of the iron passes through the fabric or textile to the adhesive, melting the same and forming a bond once the heat source is removed and the hot melt allowed to cool. However, care must be taken in forming the seam so as to avoid scorching the fabric or even melting of the fabric (especially in the case of certain fabrics of low temperature synthetic polymers and elastomeric materials) with the hot iron as well as leakage or squeeze-out of the adhesive from the edges of the tape. Furthermore, if adhesive leaks through the seam or bleeds through the rolled good itself and comes in contact with the hot iron, noxious fumes may arise and, more importantly, the iron may no longer be suitable for its traditional use of pressing or ironing articles of clothing and the like.
The problems associated with the use of adhesive tapes are compounded and magnified in the seaming, particularly butt end seaming, of heavy duty, thick fabrics as used for tapestries and curtains and especially in the seaming of carpets. For convenience, the following discussion will be directed to carpet seaming. Carpet seaming tapes are generally 3-6 inches in overall width and are comprised of a heat-activated adhesive coated in the central 2-5 inches of these tapes, preferably a hot melt adhesive, a reinforcing fabric, and a carrier paper, oftentimes coated with a silicone release coating on the backside. A general schematic of the traditional carpet seaming tape is shown in FIG. 1 where the tape 1 includes a paper backing 2, often creped and frequently coated with silicone release coating on the reverse side 4, a reinforcement strip or scrim 3 for strength and a thermally activatable adhesive 5. Reinforcement strip 3 can be a knit or woven material and may extend to the edge of the tape but is frequently ½ to 1 inch narrower than the paper carrier leaving equal spacing on each edge. The adhesive may be in the form of a layer or beads or a combination thereof, but, in any event, is placed a set distance from the edges of the tape to prevent the molten adhesive from flowing off the tape and inadvertently bonding the carpet to the pad during the heating and subsequent pressing steps. If this should occur, the silicone release coating on the underside of the tape ensures that the tape itself will not bond to the padding, although this will not prevent the back of the carpet adjacent to the tape from bonding to the pad.
This seaming method requires the operator to first place the seaming tape, adhesive side up, directly under the open seam defined by the opposing edges of the carpeting. Once the carpet and tape are properly aligned, the operator then lifts the carpet and inserts a specialized heating iron, whose lower surface is elevated to a sufficient temperature to activate or melt the adhesive, underneath the carpet and in direct contact with the heat activated adhesive of the seaming tape. Once the underlying adhesive has been melted or reacted, the hot iron is advanced along the seam to heat the next section of adhesive. Concurrently, the trailing edges of the carpet behind the iron are brought in contact with the molten adhesive, manipulated to mate opposing edges of the carpeting to match any designs that may be incorporated into the carpet, and then pressed into the molten adhesive to ensure good surface contact and integration of the molten adhesive into the rough surface of the carpet backing. Thereafter, the adhesive is allowed to cool to form the bonded seam. The desired outcome is a seam that is not distinguishable from the rest of the carpet when viewed from the top of the carpet after the carpet has been stretched onto a tack strip or like device that holds the finished carpet in place.
Though the foregoing is the most commonly practiced method of carpet seaming, it is not without its disadvantages. One particular disadvantage is the incidence of peaking of the carpet at the seam once the carpet is stretched. Numerous improvements to the carpet seaming tapes have been proposed for addressing this problem including the use of multiple tapes in a side-by-side relationship (Johnston et. al. U.S. Pat. No. 4,749,433), extra-wide tapes (Johnston et. al. U.S. Pat. No. 4,919,743), and plastic or metallic reinforcing elements (Matthews U.S. Pat. No. 5,691,051 and U.S. Pat. No. 6,110,565 and Matthews et. al. U.S. Pat. No. 5,198,300). Others have proposed the use of an excess of adhesive at the centerline of the tape. One way in which this has been achieved is through the use of specialized irons that include channels or channeling features on their lower surface which divert molten adhesive so as to create a ridge of excess adhesive directly under the seam. While all of these provide some relief to the peaking problem, they do so at the expense of added costs in relation to the materials and manufacturing of the tapes and/or tools.
While the modified irons would seem a most efficient means to ensure additional adhesive at the seam, they are not without problems and shortcomings. Most notably, if the adhesive is heated significantly above its melting point, its viscosity becomes so low that a substantial amount may flow away from the ridge region as the tool is advanced and before the applicator can properly align and place the carpet edges. Additionally, because the adhesive in the formed ridge area is exposed to the air for the longest period of time, cooling will result in some solidification or viscosity build up in the adhesive in this area so that even if the applicator can ensure that adhesive is present at the interface of the abutting edges, surface wetting may not be sufficient to ensure a strong bond at the interface, i.e., by the time the applicator is able to align and place the carpet edges in proper position and press the same into the adhesive, the adhesive may not be viscous enough to flow into the interface between the abutting edges and/or to develop a sufficiently strong bond with the consequence that when the carpet is stretched the abutting edges separate or open: much like a paper cut opens when one pulls the skin on opposite sides of the cut in opposite directions.
In addition to the foregoing problems, the hot iron method does not allow for ease of redoing a seam once formed. Should the applicator find the pattern is off or that a gap exists in the seam bond, he must employ extreme care in reopening the seam to the point of the problem. In this method, the only way to open the seam is to rip it apart and then strip the tape from the back of the carpet. This process can severely damage the carpet and the carpet backing. Similarly, this method and tool do not allow for simple repairs in the event one needs to replace a small section of carpeting, for example to repair a cigarette burn, or to re-bond a small segment of the seam that has opened due to traffic. In essence, one must open an area sufficiently large to enable the tool to be placed under the carpet and removed. Furthermore, the heat of the tool often causes a relaxation of the twist of the carpet pile resulting in a noticeable difference in the carpet texture at the seam.
Besides the aforementioned difficulties with the process, the hot iron method has a number of additional concerns as well, including health and safety related concerns. For example, the hot iron generates the emission of strong, offensive fumes from the adhesive. Additionally, because the irons, during use, generate a build up of adhesive and adhesive residue on the underside of the iron, i.e., that side in contact with the adhesive, the operator must often raise the temperature of the tool periodically during the seam forming operation in order to ensure good melting/activation of the adhesive. This can even occur during a single seam forming operation where it is not possible to interrupt a seaming operation to remove and clean a tool without seriously risking problems. As noted above, such higher temperatures result in lower viscosities of the adhesives, increasing the likelihood that adhesive will leak beyond the tape edges and bond the carpet and/or the tape to the underlying pad or flooring as well as through the tape backing itself. Additionally, such hot irons can permanently distort the carpet backing as well as the carpet structure itself as a result of scorching or, in the case of polymer based materials, melting and/or relaxation of the carpet fiber twist; cause severe burns in workers who accidentally touch or come in contact with the hot surface of the iron; cause the emission of noxious fumes as a result of the melting and scorching of the adhesive. Additionally, a build up of adhesive and adhesive residue on the iron interferes with the heat transfer from the iron to the adhesive, thus slowing down the overall seaming process and unduly extending the time needed to complete the job.
A number of alternative technologies have been developed in an effort to address some of the problems with the traditional irons and seaming techniques. In particular, concerns relative to adhesive buildup on the iron and the concomitant need for higher temperatures for the iron, and the associated problems with such higher temperatures, are eliminated by seaming methods and devices wherein the heat needed for activating or melting the adhesive is generated within the seaming tape itself and no tools come in direct contact with the adhesive. Additionally, these alternative methods involve tools that do not become excessively hot in use and, thus, concerns for burns to the applicator or the carpet are not an issue. Further these alternative technologies do not involve the use of tools which travel beneath the carpet and above the seam tape, thus making the seaming method much easier.
One of the alternative methods involves resistance heating as a means of melting or activating the adhesive. For example, Brooks (U.S. Pat. No. 4,416,713), Middleton (GB 1,499,801) and Rodenbaugh (GB 1,507,851) each teach methods of carpet seaming using electrically conductive seaming tapes, i.e., seaming tapes similar to those used in traditional iron seaming methods except that they have an electrically conductive resistance element incorporated into the tape. In practice, each end of the tape is connected to an electrical current supply source to create a circuit. Heat generated by resistance heating as the current passes through the conductive element then melts or activates the adhesive. This eliminates many of the problems with the hot iron method and device but creates additional problems as mentioned below.
Because the tape is activated for the whole length of the seam at once, special care must be taken to ensure that the whole seam is properly aligned before inducing the current. Any movement of the carpet before the seam is cured or set, even as a result of a misstep by the applicator at or near the seam, may throw the entire seam out of alignment. Additionally, any break in the conductive element in the tape will render the entire length of the conductive seaming tape ineffective. In this respect tears or breaks in the conductive material may occur during the manufacture of the tape, in the course of laying the tape and carpet or as a result of forces pressing down on the tape after its placement, e.g., as a result of a misstep or the placement of a heavy and/or sharp edged article on the seam. More importantly, this method requires costly, bulky and inconvenient current supply equipment capable of generating currents of over 100 amps in order to generate sufficient heat along a lengthy seam to sufficiently heat the adhesive.
To some extent the need for bulky and costly equipment may be addressed by superimposing one strip of the conductive material over another with an intervening electrically insulating material, isolating the one from the other, (Brooks U.S. Pat. No. 4,610,906) or by placing two narrow strips of conductive material in a spaced, side-by-side relationship along the length of the seaming tape (Baxter AU57288/80). In use, a conductive bridge is applied linking each conductive strip to the other at one end of the tape and the leads from the power source are attached to the conductive strips at the opposing end of the tape. Both tapes present problems of manufacture and handling to ensure that the conductive strips do not touch each other. In the latter, the strips must be placed carefully to ensure they do not touch; whereas in the former, care must be taken to ensure that nothing pierces the tape, a happenstance that could create a short through the electrically insulating layer. Furthermore, because the heat generated by the conductive material is fairly constant along the conductive element and across its width (assuming uniformity in the material), the use of thicker regions of adhesive can create problems as the time to melt the adhesive in such regions is longer than in thinner regions. Thus, the adhesive in the thinner regions will achieve a lower viscosity and have a greater tendency to flow before the adhesive in the thicker regions is sufficiently melted to effectively bond the carpet. This can lead to leakage of the adhesive from the seam.
A second alternative carpet seaming technology relies upon induction heating and induction activatable seaming tapes. Induction activatable seaming tapes are similar, in many respects, to the resistance tapes except that heating results from eddy currents and hysteresis effects that are induced in a susceptor material, e.g., a foil layer or strip, upon being exposed to electromagnetic fields. Although Middleton (GB 1,499,801) primarily focused on resistance tapes wherein the conductive medium is a perforated conductive foil, Middleton also indicates that these tapes may be activated by induction. Nakano (EP 0237657) also teaches carpet seaming using induction activatable adhesive tapes that are activatable upon exposure to alternating magnetic fields of high frequency. Finally, Sakai et. al. (JP 1200937 and JP1203825) teach induction heating apparatus and induction carpet bonding methods wherein the induction tool for generating the high frequency magnetic field has three circular coils in a linear relationship corresponding, in use, to the centerline of the seaming tape. It is believed that this technology was commercialized by Hiroshima in Japan; however, it has since been removed from the market due to poor performance and acceptance of the product.
While induction seaming methods as taught in the prior art will address many of the issues and detriments of the iron seaming method and the resistance seaming method, they still have various shortcoming of their own. For example, leakage of activated or melted adhesive from the edge of the tape is still of concern, especially if the adhesive as applied to the tape is close to the edge. More importantly, induction tools and induction activatable tapes taught to date for use in carpet seaming suffer from poor heating in the area of the scam line or centerline. With such tapes and tools, the prominent heating occurs at the edge of the susceptor and not at the centerline of the susceptor. Indeed, the traditional induction tools taught in the aforementioned art provide little, if any, heating at the centerline of the tape due to the fact that the induced electric field and heating is very weak directly under the center of the coil. Since the carpet seam itself overlies the centerline of the tape, that area of the seam that most needs heat to ensure a good bond receives the least amount of heat. Consequently, there can be unbonded gaps or weaknesses in the seam as a result of incomplete or insufficient heating of the adhesive directly under the seam. Although activation of the induction tool for longer periods of time may allow additional heat to traverse the tape to the centerline, in reality this is not likely to occur to any significant extent since the more ready direction of heat transfer is through the foil to the other layers of the tape and carpet rather than across the thin foil. Consequently, even if such transverse heating were possible, by the time sufficient heat transferred to the centerline area, the other components of the tape and carpeting in contact with those regions of the tape where heating was effected, particularly at or near the edges of the susceptor, would suffer from excessive heating resulting in scorching and burning of the adhesive, other tape components and/or the carpeting. These problems are even further magnified and compounded if the tapes employed thicker adhesive regions in the centerline area.
Thus, there remains a need in the art to design heat activatable tapes that lessen or eliminate the concern for adhesive leakage or squeeze-out, without increasing, or substantially increasing, the costs of the tape.
There also remains a need in the art to design tapes which are readily activatable by induction and provide suitable, durable carpet seams and, in a preferred respect, have thick regions of adhesive in the centerline to enhance butt end bonding and reduce the likelihood of peaking without being concerned that excessive induction times and heat would be needed and without risking scorching or burning of the tape, the carpet backing or even the carpeting itself.
There also remains a need in the art to design induction seaming systems whereby induction tools and tapes are specifically designed for use in combination so as to provide enhanced performance, whether for addressing adhesive leakage or squeeze-out, peaking or merely for improving bonding in the centerline region of the tape without overheating the edges of the tape.